1. Field of the Invention
The present invention relates to a vehicular air bag device which is to be disposed in a vehicle such as an automobile, and more particularly to a hinge structure of a door member.
2. Description of the Related Art
A vehicle such as an automobile is provided with an air bag device as safety means for a collision of the vehicle. Such an air bag device operates in the following manner. When an impact force which is larger than a predetermined level is applied to the vehicle body by a collision of the vehicle, the air bag body which is housed in a folded condition in an interior part such as an instrument panel is inflated toward a passenger in a cabin by supplying a high-pressure gas from an inflator, to receive the passenger, thereby protecting the passenger from a secondary collision against the instrument panel or the like.
The air bag body is configured so as to, when inflated, press an air bag lid portion which is made of a resin, and which is formed in the instrument panel or the like, whereby a score groove which is previously formed in the rear face of the air bag lid portion is broken and a door piece is opened. As a result, an inflation opening is formed so that the air bag body can be inflated toward the passenger in the cabin.
In the air bag device, a door member made of a metal is disposed on the rear face side of the door piece, whereby conflicting functions of ensuring the strength which can withstand the pressing force exerted from the surface side of the single-layer or multi-layer resin-made air bag lid portion, and of ensuring the breaking at the score groove are enabled to be inconsistent with each other.
Recently, an air bag device having the following configuration is proposed. An inflator is designed so as to cope with both a conventional operation mode (in which the whole of a predetermined amount of gas is ejected by a single ejecting operation) and a multi-stage operation mode (in which a predetermined amount of gas is stepwise ejected by plural ejecting operations), and to be selectively set to the conventional operation mode or the multi-stage operation mode. In the proposed air bag device, however, a special hinge structure is required which can cope with both the conventional operation mode and the multi-stage operation mode of the inflator.
When the hinge portion is set to have a large flexural rigidity which can withstand a high inflation pressure of the air bag body in the conventional operation mode of the inflator, the hinge portion is hardly bent by a low inflation pressure of the air bag body exerted by a first-stage gas ejection operation in the multi-stage operation mode of the inflator, thereby producing the possibility that a predetermined inflation opening cannot be satisfactorily formed in an air bag lid portion. By contrast, when the hinge portion is set to have a small flexural rigidity at which the hinge portion can be bent by a low inflation pressure of the air bag body exerted by a first-stage gas ejection operation in the multi-stage operation mode of the inflator, there arises the possibility that the hinge portion is broken by a high inflation pressure of the air bag body in the conventional operation mode of the inflator. As a result, hinge rotation of the door piece which is formed in the air bag lid portion may not be satisfactorily conducted.